Undoped semi-insulating (SI) InP samples, subjected to one-step and multi-step wafer annealing, and lightly and normally Fe-doped SI InP samples without annealing have been characterized by thermally stimulated current (TSC) spectroscopy. A dominant deep center at 0.63 eV is found in all samples and is undoubtedly due to iron. Two prominent TSC traps, T-b (0.44 eV) and T-d (0.33 eV), found in undoped SI InP, are thought to be related to the phosphorus antisite P-In, and traps at low temperatures, like T-e* (0.19 eV), to the phosphrus vacancy V-P.